They're so cute! Two or three, just alike – or similar enough so you can tell that they're twins or triplets. But it's not all sweet-smelling babies and identical clothing. Multiple pregnancies are considered high-risk, and the more fetuses the mother is carrying, the higher the risk to both her and her unborn children.

And with more women taking advantage of advanced reproductive technology (ART) and fertility drugs, multiple pregnancies and births are skyrocketing, according to the National Center for Health Statistics.

While the vast majority of these pregnancies (94 percent in 1997) are twins, the rates for triplets and other higher-order multiples are growing at an even faster rate. According to a paper published by Dr. Louis Keith, Dr. Susan Klock and Dr. Sanjay Gandhi, "In little more than two decades, the subject of multiple pregnancy has evolved from an obstetric curiosity to an issue of international medical and social concern."

About two-thirds of twins are not identical. Commonly called fraternal twins, the correct scientific term for these twins is dizygotic. Dizygotic twins are the result of two separate eggs being ovulated and fertilized at the same time by two different sperm, thus giving these twins each a different genetic makeup.

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